Gambusia Control Homepage

Welcome to the gambusia control homepage, dedicated
to ongoing investigation of the effect of gambusia on native aquatic
fauna, and exploration of potential means of control. This page will be
of interest to scientists, aquarists, and environmentalists. While many of
the examples here come from specific geographic regions like Australia,
New Zealand, and North America most of the issues are common across
the worldwide distribution of gambusia.

Gambusias have traditionally been referred to as mosquitofish based on
the assumption they are ideal for mosquito larvae control. While
we prefer to retain gambusia in the title to this page (since
this allows for world wide understanding), we would like to suggest
adoption of a more suitable name for these species outside their natural
range, damnbusia. This is not an effort to damn this poor innocent fish,
but to inform the masses that this species can be a major pest and in many
cases more suitable alternatives exist for mosquito larvae control. Hence
we feel the name is far more educational and valuable than the misnomer of
mosquitofish.

Many people ask what should we use for mosquito control if we can't use mosquitofish? Pretty much
any fish will eat mosquito larvae. Try finding a mosquito larvae in any body of water inhabited by
fish. The best thing to use is a native fish found in your local area that is somewhat hardy and
will reproduce in the environment that requires mosquito control. Which species this is will
totally depend upon where in the world you live, but most parts of the world have suitable species
that probably already exist in your vicinity. And please stick to using fish from your local river
basin, rather than the same or similar species brought in from outside your local river basin as
significant differences often exist between populations from different river basins.

Please
, any additional pertinent information we
could add to the page, and/or indicate if you would like to be included in
the gambusia control network (at the
end of the text). Ultimately we would like this to become a valuable
reference site for people to use in any way they can in their efforts to
improve the realms of their favourite native aquatic critters.

This concept, and the bulk of the content of this page were the original brainchild of
The page and the server it is
on are maintained by
We both add additional content as needs and time allows. Last major update was on 2nd November
1998, but additional references and links get added regularly.

Gambusia and mosquito control

Gambusia holbrooki and G. affinis (Cyprinodontiformes:
Poeciliidae) are native to southern and eastern USA, but now (following
translocation) have an extensive global distribution. Where mosquito-borne
diseases pose a threat to human health, and native fish are not suitable
control agents (such as urban areas in Thailand and Venezuela) stocking
water bodies with poeciliids (such as gambusia and guppies Lebistes
reticulatus) may be one of the few means of mosquito control. These
poeciliids are well-suited to stagnant waters, where they tend to remain
stationary just below the water surface, using the relatively oxygen-rich
interface layer. However, the effectiveness of gambusia as a mosquito
control agent is unclear. Gambusia may prefer to consume
macro-invertebrates other than mosquito larvae (particularly large
instars). Some of these macro-invertebrates consumed may include species
which also prey on mosquito larvae. Gambusia, not having the
aestivation/embryonic diapause capability of some Cyprinodontiformes, die
out in seasonal ponds, requiring a restocking program. In any event, the
larvae of many mosquito species develop in rain-filled tree hollows and
peridomestic containers, such as coconut shells and discarded packaging,
concealed from vertebrate predators.

Many examples from North America demonstrate the negative effects of
gambusia. Due in large part to predation, gambusia have eliminated Gila
topminnow (Poecilliopsis o. occidentalis) from almost it's entire
range. Populations only persist where gambusia are absent or in a few
springs where other as yet unknown ecological characters allow them to
coexist (Minckley et al. 1991). The other subspecies, the Yaqui
topminnow (P. o. sonoriensis) is also in great danger as
gambusia are only just starting to invade and spread throughout the Yaqui
River system. Gambusia have a major impact on some pupfish
(Cyprinodon spp.) populations. While no extinctions due to this
have been recorded, coexisting populutions tend to be quite depressed in
abundance. Evidence collected in part by Unmack (unpub. data) from Ash
Meadows, Nevada suggests that when gambusia are decreased in abundance by
physical removal, significantly higher numbers of pupfish occur within a
year. Gambusia have also been demonstrated to cause extinction of
California newt (Taricha torosa populations (Gamradt & Kats,
1996). Much to Diamond's amazement gambusia are freely given out to
anyone who wants them in southern California. To directly quote Diamond
(1996);

"I phoned the Los Angeles County [West Vector Control] ... District at
310-915-7370. In answer to my questions, a staff member told me: "Yes,
they would give me mosquitofish; no, there would be no cost to me; no, I
would not have to identify myself, fill out an application or explain what
I intended to do with the fish; no, the fish are harmless and present no
dangers of which I should be aware; yes, I could have 100 of
them"."

In summary, there is ample evidence that gambusia poses a threat to
endemic species in parts of Australia, New Zealand, and North America.
Hence the need to develop a gambusia control strategy. Complete
eradication is unlikely to be attainable, and may not be desirable. Some
options concerning biological agents are considered below. Other options,
including alteration of water flow rate, netting, and application of
piscicides have been trialed but are presently outside the scope of this
discussion.

The potential for biological control of
gambusia in Australia and New Zealand

Proposed biological control strategies for vertebrate pests require
thorough preliminary evaluation of the risks posed to endemic and/or
domesticated species. Cyprinodontiformes is thought to have originated in
the Cretaceous Period (Parenti, 1981) and is native to the New and Old
Worlds, west of Wallace's line. Therefore, in designing a strategy for
biological control of gambusia in Australia and New Zealand, disease
agents specific to Cyprinodontiformes could be considered.

Biological control agents vary in pathogenicity towards, and/or
specificity for, target hosts. Pathogenicity can be altered (enhanced or
attenuated) by selective passage in host or model systems, while
specificity is usually not amenable to manipulation.

Perlmutter & Potter (1987) reported a retrovirus, associated with
melanoma formation, in a poeciliid. However, there is evidence suggesting
that some viruses have jumped species barriers (including the canine
parvovirus pandemic in 1977/78, which may have evolved from the feline
enteritis virus in laboratory-maintained cats; the possible transfer of
HIV-AIDS from primates to humans in the 1960s; and the avian influenza
concern of 1997/98). Considerable expertise, and investment, is usually
required to ensure quarantine facilities function effectively. Viral
control of gambusia is not presently practical.

Many bacterial and fungal disease agents are limited spectrum
opportunist pathogens, such as Bacillus thuringiensis (toxic to
insects) and the fungus Aspergillus spp. (pathogenic to birds).
However, Saprolegnia spp. fungi commonly isolated from wounded
fish, and Vibrio spp. frequently cultured from dead fish, appear to
be non-host specific, and of enhanced pathogenicity to immune-compromised
animals.

Gambusia was reported to host at least 23 parasite species (L.
N. Lloyd, cited in Arthington & Lloyd, 1989). Many metazoan parasites
(including nematodes and some cestodes) are monoxenous (specific for one
host species), but apparently this is not the case in fish. Diseases of
fish are relatively poorly characterised, in comparison with diseases of
humans and domesticated animals, and the causative agent(s)
less-frequently identified. Hence, the apparent polyxenicity of many fish
pathogens (including parasites).

Some protozoan parasites of vertebrates are polyxenous, such as
Giardia of mammals, Toxoplasma gondii of felids,
Ichthyophthirius multifiliis (Ciliophora) of fish, and many
coccidia (Apicomplexa) of fish (Dykova & Lom, 1981; Lom & Dykova,
1995). Others coccidia are virtually monoxenous, such as some eimerian
coccidia of domestic poultry, and fish. There does not appear to be any
criteria to predict specificity.

While attention has focused on (the expansion of) successful gambusia
introductions, the factors responsible for unsuccessful introductions have
been largely unreported, or inadequately investigated. Gambusia
communities at the margin of established or recently translocated
populations may be subject to environmental stress, and prone to
parasitism. As gambusia is an omnivorous, opportunistic cannibal,
the transmission of parasites with either direct or indirect life cycles
is possible.

One concern surrounding biological control of an exotic pest is the
risk of further reduction of biodiversity, if the target species is eradicated.
If gambusia has become integrated into localised habitats, eradication
could initiate a perturbation placing further stress on extant aquatic
fauna. This concern has been raised in conjunction with rabbit eradication
strategies: it has been suggested that, as rabbit populations decline cats
and foxes would eat more native fauna.

Gambusia in its native range may be partially controlled by predators
including Fundulus spp. However, there are no reports suggesting
that, outside its native range, gambusia is other than a minor
constituent of the diet of piscivores. On the other hand, it would be
interesting to trial the effect of certain exotic predators on gambusia
(after ascertaining that such introductions would have no impact on
endemic fauna). Some of the larger Cynolebias spp. and
Nothobranchius spp. (Cyprinodontiformes) are piscivorous annuals,
restricted to seasonal pools, in which they may be able to eliminate
gambusia refuge populations. Unmack (unpub. data) and others have
observed that gambusia and larger galaxiids rarely coexist and galaxiids
eagerly devour gambusia in aquaria. In small waterbodies diadromous
galaxiids such as the common galaxiid (Galaxias maculatus) could
be introduced at high densities to predate on gambusia, then after 2-4
years the galaxiids would die of old age and since they cannot reproduce
in isolated ponds it leaves the waterbody exotic free to reestablish
native organisms in.

Conclusions

Arthington & Lloyd (1989) stated that "biological population control is
well beyond present capabilities". A decade later, the threat posed by
gambusia to the aquatic biodiversity of Australian and New Zealand
has not been ameliorated. Further research into predation of native fishes
may redefine the problem, and investigation of gambusia-specific
parasitism may suggest a solution. Proposals for gambusia control
may benefit from knowledge that gambusia is unrelated to native
fauna, omnivorous, an opportunist cannibal, and avoids fast-flowing waters.
Such schemes may further function as a model system for the eradication
of naturalised Tilapia and carp, Cyprinus carpio.

Duncan, D. K. & J. M. Voeltz. 2004. Novel application of a novel tool: using a U.S. Endangered
Species Act Safe Harbor Agreement to reduce the use of mosquitofish. Page 70 in Abstract of papers
presented at the 13th International Conference on Aquatic Invasive Species, September 20-24, 2004,
Ennis, Ireland. 283pp.

Swanson, C., Cech, J.J & Piedrahita, R.H. 1996. Mosquitofish:
Biology, Culture, and Use in Mosquito Control. Mosquito and Vector
Control Association of California and The University of California
Mosquito Research Program. pp. 88.

Willis, K. & N. Ling. 2000. Sensitivities of mosquitofish and
black mudfish to a piscicide: could rotenone be used to control
mosquitofish in New Zealand wetlands? New Zealand Journal of
Zoology. 27(2): 85-91.

The Exotic
fauna in Western Australian wetlands web page by Mark Lund has two
articles on gambusia on their effects on invertebrates in Lake
Monger, a lake near Perth in Western Australia. Just click on the
Western Australian wetlands and then the exotic fauna link to get to them.